The following shall constitute a prior art statement in accordance with the guidelines suggested in 37CFR Sections 1.56, 1.97 and 1.98.
Oil well fluids, such as those used in drilling or oil and water mixtures produced from wells, often contain large amounts of abrasives such as drilling mud solids, sand or ground rock. Such abrasives constitute a significant problem since oil well fluid handling mechanisms such as pumps and the like are subjected to extreme wear due to the presence of such abrasives in the fluids. Oil well fluid service pumps are particularly prone to extreme wear because the fluids containing abrasives pass through them in large volumes and at high flow rates. Surfaces such as valve closures within these pumps require frequent maintenance to retain adequate pumping efficiencies.
Common oil well fluid service pumps contain one or more check valves of the type in which fluid flow is interupted by a disc type closure which seats against a planar surface having one or more fluid flow passages therethrough. Since, in the open position of the valve, oil well fluids containing abrasives impinge directly on the seating face of the disc, wear on the seating face is a constant problem. In an effort to reduce maintenance of the discs of such valves, the discs are made of strong engineering thermoplastics which can withstand the heat and corrosiveness of an oil well fluid environment as well as endure the impingement of abrasives in the fluid while being relatively inexpensive. Acetal polymers such as those sold by DuPont under the trademark "DELRIN" are typical of the material provided for such use.
As an alternative to the use of high strength, engineering plastics, stainless steel discs covered with a resilient layer of rubber have been used which offer an extended service life but are significantly more expensive than acetal polymer discs.
Another major problem with the use of acetal polymer discs arises in applications where the disc is positioned on a shaft passing through the center of the disc with spring means provided to force the disc into seating engagement with the valve seat thereby closing the valve. When the valve is opened by the development of differential pressure sufficient to overcome the seating pressure of the valve spring, there can be a tilt or wobble induced in the valve disc due to any of several factors such as uneven flow through valve orifices and the like. Such wobble around the mounting shaft, particularly with regard to polymeric discs, results in extreme wear of the discs at the central opening through which the shaft passes. Loss of the pumping and valve efficiency through such failure is at least as common with this type of failure as with abrasive wear of the seating surfaces of the valve disc. Such wear is present, though to a lesser degree, on rubber-coated stainless steel valve disc closures.